Diffusion barrier layers and processes for depositing metal films thereupon by CVD or ALD processes

ABSTRACT

A process is described for depositing a metal film on a substrate surface having a diffusion barrier layer deposited thereupon. In one embodiment, the process includes: providing a surface of the diffusion barrier layer that is substantially free of an elemental metal and forming the metal film on at least a portion of the surface via deposition by using a organometallic precursor. In certain embodiments, the surface of the diffusion barrier layer may be exposed to an adhesion promoting agent prior to or during at least a portion of the forming step. Suitable adhesion promoting agents include nitrogen, nitrogen-containing compounds, carbon-containing compounds, carbon and nitrogen containing compounds, silicon-containing compounds, silicon and carbon containing compounds, silicon, carbon, and nitrogen containing compounds, and mixtures thereof. The process of the present invention provides substrates having enhanced adhesion between the diffusion barrier layer and the metal film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/428,447 U.S. Pat. No. 7,311,946, filed 2 May 2003, andissued Dec. 25, 2007, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to a diffusion barrier layer and methodcomprising same upon which a metal film, preferably a copper film, isdeposited thereupon. More specifically, the present invention relates toa diffusion barrier layer and method comprising same that improves theadhesion between the diffusion barrier layer and the metal layer.

As the microelectronics industry evolves into ultra-large-scaleintegration (ULSI), the intrinsic properties of typical metallizationmaterials become the limiting factor in advanced circuit design andmanufacture. Aluminum, which has been widely used as the interconnectmetal, suffers from several drawbacks such as relatively high electricalresistivity and susceptibility to electromigration which may curtail itsusefulness. Other metallization materials, such as tungsten andmolybdenum, provide a high migration resistance but also have a highelectrical resistance that prevents an integrated circuit incorporatingthese materials from being operated at high speed. Because of its lowresistivity and enhanced resistance to electromigration, copper is anattractive material for high-speed integrated circuits. Still othercandidates being considered for use as a metallization material includeplatinum, cobalt, nickel, palladium, ruthenium, rhodium, iridium, gold,silver and alloys comprising same.

Numerous methods such as ionized metal plasma (IMP), physical vapordeposition (PVD), chemical vapor deposition (CVD), atomic layerdeposition (ALD), plasma-assisted chemical vapor deposition (PACVD),plasma-enhanced chemical vapor deposition (PECVD), electroplating, andelectroless plating have been used to deposit a metal film such ascopper upon a barrier layer. Among them, CVD and ALD methods using oneor more organometallic precursors may be the most promising methodsbecause these methods provide excellent step coverage for high aspectratio structures and good via filling characteristics.

Several organometallic precursors have been developed to deposit lowelectrical resistivity copper films by the aforementioned processes,particularly CVD or ALD processes. Two of the most useful families ofcopper CVD precursors that have been studied extensively are the Cu (I)and Cu (II) β-diketonates. The Cu (II) precursors require use of anexternal reducing agent such as hydrogen or alcohol to deposit copperfilms that are largely free of impurities, while Cu (I) precursors candeposit pure copper films without using an external reducing agent via abimolecular disproportionation reaction that produces a Cu (II)β-diketonate as a volatile byproduct. The β-diketonate ligand most oftenpresent in these precursors is hexafluoroacetylacetonate or the hfacanion [OC(CF₃) CHC(CF₃) O]⁻. A particularly effective CVD copperprecursor is 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato-copper (I)trimethylvinylsilane (hereinafter Cu(hfac)(tmvs)), which is sold underthe trademark CUPRASELECT™ by the Schumacher unit of Air Products andChemicals, Inc., Carlsbad, Calif., the assignee of the presentinvention.

A barrier layer is typically utilized in conjunction with a metal orcopper layer to prevent detrimental effects caused by the interaction ordiffusion of the metal or copper layer with other portions of theintegrated circuit. Exemplary barrier materials include metals, such astitanium, tantalum, tungsten, chromium, molybdenum, zirconium, vanadium,and carbides, nitrides, carbonitrides, silicon carbides, siliconnitrides, and silicon carbonitrides of these metals where theyconstitute a stable composition. In some instances, the initialdeposition of CVD or ALD metal or copper film on the barrier layer mayfunction as a seed layer, e.g., an adhesive, conducting seed layer tofacilitate further deposition of a subsequent metal layer such as copperby electrochemical plating, electroless plating, or by PVD, CVD, or ALDmethods to complete the thin-film interconnect.

Despite the foregoing developments, the integrated circuit (IC) industryis presently experiencing difficulty forming adherent metal or copperfilms on diffusion barrier layer materials. A variety of solutions tothis problem have been proposed. For example, Gandikota et al.,Microelectronic Engineering 50, 547-53 (2000), purports to improveadhesion between a CVD copper thin film and barrier layers by: (a)depositing a copper flash layer on the barrier layer by physical vapordeposition (PVD) prior to chemical vapor deposition, or (b) annealingthe CVD copper layer after deposition. See also Voss et al.,Microelectronics Engineering 50, 501-08 (2000). Unfortunately, thesemethods are not acceptable to the IC industry because they add to theequipment requirements for the copper deposition step. In addition,annealing, particularly at elevated temperatures, can have deleteriouseffects on the overall product.

U.S. Pat. No. 5,019,531 discloses a CVD process for depositing copper ona substrate selected from the group consisting of aluminum, silicon,titanium, tungsten, chromium, molybdenum, zirconium, tantalum, vanadiumand suicides thereof using an organic complex or organometallic compoundof copper. The organic complex or organometallic compound is selectedfrom β-diketonate and cyclopentadienyl compounds of copper such asbis-acetylacetonato-copper, bis-hexafluoroacetylacetonato-copper,bis-dipivaloylmethanato-cooper, dimethyl-gold-hexafluoroacetylacetonato,cyclopentadienyl-triethylphosphine-copper, anddimethyl-gold-acetylacetonato. The adhesion of the copper on thesubstrate, however, was poor.

As mentioned previously, one method to form a copper film unto asubstrate having a barrier layer deposited thereupon is through plasmaenhanced or plasma assisted chemical vapor deposition. The reference,Eisenbraun et al., “Enhanced Growth of Device-Quality Copper by HydrogenPlasma-Assisted Chemical Vapor Deposition” published in Appl. Phys.Letter, 1992), describes a PACVD process for depositing copper usingβ-diketonate precursors. According to Eisenbraun, the copper precursoris reduced by atomic and ionic hydrogen species to deposit copper on thesubstrate. The reference, Jin et al., Plasma-Enhanced Metal OrganicChemical Vapor Deposition of High Purity Copper Thin Films Using PlasmaReactor with the H Atom Source” published in J. Vac. Sci. Technology A,1999, also discloses a plasma-enhanced technique to deposit pure copperusing Cu(II) bis(hexafluoroacetylacetonato), Cu(II)(hfac), as anorganometallic precursor. Likewise, the reference, Laksmanan et al., “ANovel Model of Hydrogen Plasma Assisted Chemical Vapor Deposition ofCopper” and published in Thin Solid Films, 1999, describes ahydrogen-plasma assisted process for depositing copper on a barrierlayer. Although, the aforementioned references were successful indepositing a metallic, continuous, dense device-quality copper film withconformal step coverage that was virtually free from heavy elementcontaminants, the adhesion of copper on the substrate was unacceptable.

U.S. Pat. Nos. 5,085,731, 5,094,701 and 5,098,516 (referred tocollectively as Norman) describe a thermal CVD process for depositing acopper film with low electrical resistivity by using a volatile liquidorganometallic copper precursor such as Cu(hfac)(tmvs) at relatively lowtemperatures onto metallic substrates. Further, the reference, Norman etal. “Chemical Additives for Improved Copper Chemical Vapor DepositionProcessing”, Thin Solid Films, 1995, describes the use of tmvs and hfacligands alone or in combination with water to improve deposition ofcopper. This deposition was achieved, however, with limited success.Numerous other researchers investigated the use of tmvs and hfac ligandsalone or in combination with water to improve deposition of copper withlimited or no success (e.g., Petersen et al. “Enhanced Chemical vaporDeposition of Copper from (hfac)Cu(TMVS) Using Liquid Coinjection ofTMVS”, J. Electrochem. Soc., 1995; Gelatos et al. “Chemical VaporDeposition of Copper from Cu⁺¹ Precursors in the Presence of WaterVapor” Appl. Phys. Letter, 1993; Japanese Unexamined Patent PublicationJP 2000-219968A; and U.S. Pat. No. 6,165,555).

Other organometallic copper precursors, such as (hfac)Cu(I)(MP) where MPis 4-methyl-1-pentene and (hfac)Cu(I)(DMB) where DMB is3,3-dimethyl-1-butene, have been used to deposit low resistivity copperfilms on silicon wafers coated with titanium nitride (Kang et al.,“Chemical Vapor Deposition of Copper Film”, Thin Solid Films, 1999). Inthe reference, Hwang et al., “Surfactant-Catalyzed Chemical VaporDeposition of Copper Thin Films”, Chem. Mater., 2000, a submonolayer ofiodine has been used to facilitate deposition of copper films fromCu(hfac)(tmvs) with a smooth surface and at a greatly enhanced rate.None of these techniques, however, discusses the quality of the CVDdeposited copper film on the barrier layer.

U.S. Pat. No. 6,423,201 B1 describes the use of a thin silicon layer atthe top of a TiN barrier layer to improve adhesion. It is, however, notdesirable to deposit copper directly on silicon due to the formation ofcopper silicon alloys which exhibit high resistivity.

The adhesion of copper to the underlying barrier materials has also beenreported to be problematic by several researchers. For example, thedeposition of copper on titanium nitride substrate usingCu(I)(hfac)(tmvs) precursor (or CUPRASELECT™) has been reported to bepoor (Nguyen, T. and Evans, D. R., “Stress and Adhesion of CVD Copperand TiN”, Mat. Res. Soc. Symp. Proc., 1995 and Nguyen, T. and Evans, D.R., “Stress and Adhesion of CVD Copper and TiN”, Mat. Res. Soc. Symp.Proceeding, 1995). It has been reported that the direct deposition ofCVD copper on a diffusion barrier leads to the formation of a fluorine,carbon and oxygen containing amorphous layer between the copper film andbarrier layer that is responsible for poor adhesion, as discussed byKroger, R. et al. in papers “Nucleation and Growth of CVD Copper Films”published in Mat. Res. Soc. Symp. Proceeding, 1999 and “Properties ofCopper Films Prepared by Chemical Vapor Deposition for AdvancedMetallization of Microelectronic Devices” published in J.Electrochemical Society, 1999. The amorphous layer is believed to beformed during very early stages of CVD copper deposition from theby-products of the Cu (I) precursor. Similar adhesion problems onbarrier layer have been reported with Cu (II) precursors.

The reference WO 00/71550 discusses limiting the formation of afluorine, carbon and oxygen containing amorphous layer on the barrierlayer by reducing and/or eliminating the amount of fluorine present inthe copper precursors. However, these attempts have not yet resulted inthe desired results.

Reduction of copper precursors like Cu (II)bis-(2,2,6,6-tetramethyl-3,5-heptanedionate) with hydrogen and Cu (II)bis-(1,1,1,5,5,5-hexafluoroacetylactonate) hydrate with methanol,ethanol, and formalin have been tried to deposit copper by atomic layerepitaxy on a variety of barrier layers with limited success, asdescribed by Martensson and Carlsson in “Atomic Layer Epitaxy ofCopper”, J. Electrochem. Soc., 2000 and Solanki and Pathangey in “AtomicLayer Deposition of Copper Seed Layers”, Electrochemical and Solid-StateLetters, 2000.

The reference, Holloway et al. in a paper “Tantalum as a DiffusionBarrier Between Copper and Silicon: Failure Mechanism and Effect ofNitrogen Additions” published in J. Appl. Physics, 1992, relates thattantalum nitride (Ta₂N) is an excellent barrier to copper penetration.However, the reference fails to discuss the deposition of copper by CVDon tantalum nitride nor the quality of CVD copper adhesion onto thetantalum nitride.

The barrier properties of CVD and sputtered tantalum nitride have beenstudied and compared by Tsai et al. in a paper “Comparison of theDiffusion Barrier Properties of Chemical-Vapor Deposited and SputteredTaN between Cu and Si” published in J. Appl. Physics, 1996. However, thereference fails to discuss the deposition of copper by CVD on tantalumnitride nor the quality of CVD copper adhesion onto the tantalumnitride.

Despite the foregoing developments, there remains a need to develop aprocess to improve the adhesion of a metal, particularly a copper, filmdeposited on a diffusion barrier layer by CVD or ALD. Further, there isa need for a process to improve the adhesion of the metal film onto thebarrier layer without incurring additional equipment requirements or anannealing step.

All references cited herein are incorporated herein by reference intheir entireties.

BRIEF SUMMARY OF THE INVENTION

The present invention satisfies one, if not all, of the needs in the artby providing a method for forming a metal layer, preferably a copperfilm, onto at least a portion of a surface of a substrate having adiffusion barrier layer deposited thereupon. Specifically, in one aspectof the present invention, there is provided a process for forming ametal film on a surface of a diffusion barrier layer comprising:providing a surface of the diffusion barrier layer wherein the surfaceis comprised of at least one material selected from a metal, a metalcarbide, a metal nitride, a metal carbonitride, a metal silicon carbide,a metal silicon nitride, a metal silicon carbonitride, and a mixturethereof and wherein the surface is substantially free of an elementalmetal; and forming the metal film on the surface using at least oneorganometallic precursor provided that when the surface of the diffusionbarrier layer (i) has a material that is the metal, (ii) has anorientation other than a preferred (111) orientation, (iii) has lessthan 95% preferred (111) orientation and/or (iv) has a material that isselected from a metal carbide, a metal nitride, and a metal carbonnitride and has less than a stoichiometric amount of nitrogen and/orcarbon atoms relative to metal atoms contained therein; then the step ofexposing the surface of the diffusion barrier layer to at least oneadhesion promoting agent selected from a nitrogen, a nitrogen-containingcompound, a carbon-containing compound, a carbon and nitrogen containingcompound, a silicon-containing compound, a silicon and carbon containingcompound, a silicon, carbon, and nitrogen containing compound, and amixture thereof is conducted.

In another aspect of the present invention, there is provided a processfor forming a substantially continuous copper film on a surface of adiffusion barrier layer comprising: providing a substrate comprising thesurface of the diffusion barrier layered wherein the surface of thediffusion barrier layer is comprised of at least one material selectedfrom a metal, a metal carbide, a metal nitride, a metal carbonitride, ametal silicon carbide, a metal silicon nitride, a metal siliconcarbonitride, and a mixture thereof; exposing the surface of thediffusion barrier layer to an adhesion promoting agent selected from thegroup consisting of nitrogen, a nitrogen-containing compound, acarbon-containing compound, a carbon and nitrogen containing compound, asilicon-containing compound, a silicon and carbon containing compound, asilicon, carbon, and nitrogen containing compound, and mixtures thereof;and forming the copper film on the at least a portion of the surface viathe deposition with an organometallic copper precursor.

In another aspect of the present invention, there is provided a processfor forming a substantially continuous metal film on a surface of adiffusion barrier layer comprising: providing a substrate comprising thesurface of the diffusion barrier layer wherein the surface of thediffusion barrier layer is comprised of at least one material selectedfrom a metal carbide, a metal nitride, a metal carbonitride, a metalsilicon carbide, a metal silicon nitride, a metal silicon carbonitride,and a mixture thereof and wherein the surface comprises a substantially(111) preferred orientation and forming the metal film on the surface ofthe diffusion barrier layer via the deposition with an organometallicprecursor.

In yet another aspect of the present invention, there is provided aprocess for forming a substantially continuous metal film on a surfaceof a diffusion barrier layer comprising: providing a substratecomprising the surface of the diffusion barrier layer wherein thesurface of the diffusion barrier layer is comprised of at least onematerial selected from the group consisting of a metal, a metal carbide,a metal nitride, a metal carbonitride, a metal silicon carbide, a metalsilicon nitride, a metal silicon carbonitride, and a mixture thereof;exposing the surface to an adhesion promoting agent selected fromnitrogen, a nitrogen-containing compound, a carbon-containing compound,a carbon and nitrogen containing compound, a silicon-containingcompound, a silicon and carbon containing compound, a silicon, carbon,and nitrogen containing compound, and mixtures thereof; and growing ametal film on the surface of the diffusion barrier layer by contactingthe surface with a halogen-containing precursor and an organometallicprecursor wherein the halogen and the metal within the precursors reactto form a metal halide layer; and exposing the metal halide layer to areducing agent to provide the metal film.

In another aspect of the present invention, there is provided a processfor forming a substantially continuous metal layer on an at least onesurface of a diffusion barrier layer, the process comprising: providinga substrate comprising at least one surface of the diffusion barrierlayer within a vacuum chamber wherein at least one surface of thediffusion barrier layer is substantially free of an elemental metal;introducing an at least one organometallic precursor into the vacuumchamber; and applying energy to the at least one organometallicprecursor to induce reaction of the organometallic precursor to depositthe substantially continuous metal layer on the at least one surface ofthe diffusion barrier layer.

In a still further aspect of the present invention, there is provided aprocess for forming a substantially continuous metal film on a surfaceof a diffusion barrier layer comprising: providing a substratecomprising a surface of the diffusion barrier layer wherein the surfaceis comprised of at least one material selected from a metal carbide, ametal nitride, a metal carbonitride, and a mixture thereof and whereinthe surface comprises a stoichoimetric amount or greater of nitrogenand/or carbon atoms relative to metal atoms contained therein; andforming the metal film on the surface of the diffusion barrier layer viathe deposition with an organometallic precursor.

In a still further aspect of the present invention, there is provided aprocess for forming a substantially continuous metal film on a surfaceof a diffusion barrier layer comprising: providing a substratecomprising a diffusion barrier layer having a surface wherein thesurface is comprised of at least one material selected from astoichiometric tungsten nitride with a (100) preferred orientation, astoichiometric tungsten nitride with a (111) preferred orientation, astoichiometric tungsten nitride which is amorphous, a stoichiometrictungsten nitride which is polycrystalline, a non-stoichiometric tungstennitride having a greater amount of nitrogen atoms than tungsten atomscontained therein, and a mixture thereof; and forming the metal film onthe surface of the diffusion barrier layer via the deposition with anorganometallic precursor.

These and other aspects of the present invention will be more apparentfrom the following description.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for depositing a metal film on asubstrate surface having a diffusion barrier layer wherein the metalfilm is deposited on the barrier layer by the chemical vapor depositionor atomic layer deposition with an organometallic precursor. Theresultant metal film may have an increased adherence to the underlyingbarrier layer. The prior art has disclosed a variety of methods fordepositing metal films, such as copper films, onto surfaces of asubstrates and/or barrier layers using an organometallic precursors,particularly fluorinated precursors. The resultant films of the priorart, unfortunately, have relatively poor adherence to the underlyingdiffusion barrier layer.

The problem of poor adherence of the metal film onto the surface of thediffusion barrier layer may be attributable to the presence of CF₃radicals on the surface of the barrier layer when a fluorinatedorganometallic precursor is used to deposit the metal layer. Inembodiments wherein a copper film is deposited, the deposition of thediffusion barrier layer and the copper layer is generally conducted in acluster tool equipped with a number of chambers operated under vacuum.The barrier layer can be deposited onto a substrate such as a siliconwafer either by CVD, ALD, or PVD in one chamber and then transferred toanother chamber for the deposition of the copper film. Because priordepositions of organometallic copper precursor have been conductedwithin the chamber, the chamber may be contaminated with fragments ordissociated species of the organometallic copper precursor such as CF₃radicals. The CF₃ radicals may react with the exposed metal in thebarrier layer, leading to the formation of a fluorine, carbon and oxygencontaining amorphous layer between the copper film and the barrierlayer. The formation of this amorphous layer may thereby compromise theadhesion between these two layers.

As mentioned previously, one particularly preferred fluorinatedorganometallic copper precursor is Cu(I)(hfac)(tmvs). While notintending to be bound by theory, there are believed to be two mechanismsinvolved when depositing copper using Cu(I)(hfac)(tmvs). The firstmechanism may be a simple disproportianation reaction wherein copper isdeposited on a substrate surface that is not chemically active towardsthe precursor and will not necessarily break the C—CF₃ bonds containedin the ‘hfac’ ligand. The product from the disproportionation reactionsuch as Cu(II)(hfac)₂ may be volatile in nature and can be removed fromthe chamber without further disintegration leaving elemental Cu to bedeposited onto the substrate surface. The second mechanism, however,which is encountered when the precursor is introduced to a barriermaterial such as tantalum which is chemically reactive and involves thebreakdown of the C—CF₃ bonds in the Cu(I)(hfac)(tmvs) molecule. Thisprocess may produce fragments such as CF₃ radicals that are extremelyreactive thereby causing the formation of an undesirable amorphous layerof chemical debris on the barrier layer surface. Consequently, it may bedesirable to avoid the breakdown of Cu(I)(hfac)(tmvs) molecule duringthe deposition process. Alternatively, it may be desirable to make atleast a portion of the barrier layer surface non-reactive to thefragments or dissociated species of the Cu(I)(hfac)(tmvs) molecule todeposit the copper film on at least a portion of the surface of thebarrier layer with improved adhesion. While the previous examplediscusses depositing copper films with a organometallic copperprecursor, it is believed that the method disclosed herein is applicableto the deposition of other metal films besides copper such as platinum,nickel, cobalt, palladium, ruthenium, rhodium, iridium, gold and silver,etc. with organometallic precursors such as organometallic platinumprecursors, organometallic nickel precursors, organometallic cobaltprecursors, organometallic palladium precursors, organometallicruthenium precursors, organometallic iridium precursors, organometallicgold precursors, organometallic silver, etc.

One attempt to render the surface of the barrier layer non-reactive tothe dissociated species of the organometallic precursor is by thedeposition of a thin, flash layer of metal onto the barrier layer usinga physical vapor deposition technique such as sputtering. The thin layerof metal may be chemically inert towards the dissociated species of theorganometallic precursor thereby preventing the formation of a fluorine,carbon and oxygen containing amorphous layer on the metal film.Unfortunately, the addition of a chamber to the production line todeposit a flash layer of metal may be prohibitively expensive. Further,the flash layer of metal is an incomplete solution to the adherenceproblem because the flash layer resides primarily at the base of deeplyetched features such as vias or lines. The sidewalls of these featuresare still exposed to the organometallic precursor in subsequentprocessing steps. Therefore, the key to achieving adhesion between themetal and barrier layer is to render the barrier layer substantiallyunreactive towards the dissociated species of the organometallicprecursor.

The method disclosed herein improves the adhesion of a metal film,preferably a copper film, upon at least a portion of the surface of thediffusion barrier layer by providing at least a portion of the surfaceof the diffusion barrier layer that may be substantially non-reactive tothe fragments of the dissociated organometallic precursor molecule.Further, in some embodiments, the breakdown of the organometallicprecursor into dissociated species may be avoided. It is thus surprisingand unexpected that the deposition of a substantially continuous metalfilm onto at least a portion of the surface of the barrier layer havingrelatively good adhesion may be achieved by avoiding exposure of anelemental metal present on the surface of the barrier layer to theorganometallic precursor and/or any dissociated fragments of theorganometallic precursor. In this connection, at least a portion of thebarrier layer surface may be substantially free of an elemental metal. Asubstantially metal-free barrier layer surface may be achieved through:(a) providing a barrier layer comprised of a metal nitride, a metalcarbide, a metal carbonitride, a metal a silicon carbide, a metalsilicon nitride, a metal silicon carbonitride, or a mixture thereofhaving a substantially (111) preferred orientation (i.e., at least 95%or greater (111) preferred orientation); (b) providing a diffusionbarrier layer comprised of a metal nitride, a metal carbide, a metalcarbonitride, or a mixture thereof barrier layer having a stoichoimetricamount or greater of nitrogen and/or carbon atoms relative to metalatoms contained therein; (c) exposing a metal nitride, metal carbide,metal carbonitride, metal silicon carbide, a metal silicon nitride, or ametal silicon carbonitride barrier layer with a (111) preferredorientation below 95% to an adhesion promoting agent prior to theformation of the metal layer; (d) exposing a surface of the metalnitride, metal carbide, metal carbonitride, a metal silicon carbide, ametal silicon nitride, or a metal silicon carbonitride barrier layerwith an orientation other than a (111) preferred orientation with anadhesion promoting agent prior to the formation of the metal layer; and(e) exposing the surface of a metal barrier layer to an adhesionpromoting agent prior to the formation of the metal layer. Examples oforientations other than a (111) preferred orientation include, but arenot limited to, a (100) preferred orientation, an amorphous layer, or apolycrystalline layer.

The adhesion promoting agent may be at least one agent selected from thegroup consisting of nitrogen, nitrogen-containing compounds such asammonia, carbon-containing compounds such as methane, ethane, propane,ethylene, acetylene, propylene, etc., carbon and nitrogen containingcompounds such as amines, silicon-containing compounds such as silaneand disilane, silicon and carbon containing compounds such as methylsilane, dimethyl silane, trimethyl silane, etc., and silicon, carbon,and nitrogen containing compounds such as trimethylsilylcyanide,1-trimethylsilylimidazole, etc., or mixtures thereof. Minimizing thecontact of the exposed metal on the surface of the barrier layer to theorganometallic precursor, particularly dissociated species of anorganometallic precursor, can minimize or eliminate the formation of theundesirable amorphous layer thereby resolving the adhesion problem.

The surface of the diffusion barrier layer of the present invention maybe comprised of a material such as a metal, a metal carbide, a metalnitride, a metal carbonitride, a metal silicon nitride, a metal siliconcarbide, a metal silicon carbonitride, or a mixture thereof. In certainembodiments of the present invention, the bulk of the diffusion barrierlayer may differ than the surface layer to which the metal film isapplied. Exemplary metals suitable for use in the present inventioninclude titanium, tungsten, chromium, tantalum, molybdenum, zirconium,vanadium, or mixtures thereof. Some exemplary metal carbides includetitanium carbide, tungsten carbide, tantalum carbide, chromium carbide,molybdenum carbide, vanadium carbide, zirconium carbide, or mixturesthereof. Exemplary metal nitrides include, but are not limited to,titanium nitride, tungsten nitride, tantalum nitride, chromium nitride,molybdenum nitride, zirconium nitride, vanadium nitride, or mixturesthereof. Exemplary metal carbonitrides include titanium carbonitride(TiCN), tantalum carbonitride (TaCN), chromium carbonitride, tungstencarbonitride, molybdenum carbonitride, zirconium carbonitrides, ormixtures thereof. Exemplary metal silicon nitrides include titaniumsilicon nitride (TiSiN), molybdenum silicon nitride (MoSiN), etc.Exemplary metal silicon carbides include titanium silicon carbide(TiSiC), tungsten silicon carbide (WSiC), etc. Exemplary metal siliconcarbonitrides include silicon carbonitride, titanium siliconcarbonitride, and tantalum silicon carbonitride, etc.

The step of exposing the surface to an adhesion promoting agent can beavoided if at least one surface of the diffusion barrier layer issubstantially free of an elemental metal. For example, in oneembodiment, the at least one surface of the diffusion barrier layer maybe substantially free of an elemental metal when it is comprised of amaterial other than a pure metal (i.e., metal carbide, metal nitride,metal carbonitride, metal silicon carbide, metal silicon nitride, ormetal silicon carbonitride) and has a substantially (111) preferredorientation, i.e., has 95% or greater (111) preferred orientation. Inthese embodiments, at least a portion of the diffusion barrier surfacemay also be substantially pure, i.e., have a material purity of 95% orgreater.

In yet another embodiment, the at least one surface of the diffusionbarrier layer may be substantially free of an elemental metal when it iscomprised of a metal carbide, metal nitride, metal carbonitride ormixture thereof having a stoichiometric amount or greater of nitrogenand/or carbon atoms relative to metal atoms contained therein. Examplesof diffusion barrier layer or surface thereof having a stoichiometricamount or greater of nitrogen and/or carbon atoms relative to metalatoms contained therein include a compound having the formulaMC_(x)N_(y) wherein M is selected from titanium, tungsten, chromium,tantalum, molybdenum, zirconium, vanadium, or mixtures thereof, x and yare each individually a number greater than or equal to 0, and the sumof x+y is a number that is greater than or equal to 1. Examples ofcompounds having the aforementioned formula include, but are not limitedto, WC, TiC, TaC, CrC, VC, ZrC, MoC, WN, TiN, TaN, CrN, VN, ZrN, WCN,TiCN, and MoN. In these embodiments, the diffusion barrier layer orsurface thereof may have a substantially (111) preferred orientation, oralternatively, have a (100) preferred orientation, is amorphous, or ispolycrystalline.

In one particular embodiment, the diffusion barrier layer is comprisedof tungsten nitride. In this embodiment, the surface of the diffusionbarrier layer to which the metal film is formed may be selected from thefollowing: a stoichiometric tungsten nitride with a (100) preferredorientation, a stoichiometric tungsten nitride with a (111) preferredorientation, a stoichiometric tungsten nitride which is amorphous, astoichiometric tungsten nitride which is polycrystalline, anon-stoichiometric tungsten nitride having a greater amount of nitrogenatoms than tungsten atoms contained therein, and a mixture thereof. Inembodiments wherein the tungsten nitride is non-stoichiometric and has alesser amount of nitrogen atoms than tungsten atoms contained therein,the surface needs to be treated with an adhesion promoting agent priorto forming the metal layer.

The diffusion barrier layer can be deposited by a variety of processessuch as, but not limited to, chemical vapor deposition (CVD), atomiclayer deposition (ALD), or physical vapor deposition (PVD) processes.Some examples of CVD processes that may be used to form the barrierlayer include the following: thermal chemical vapor deposition, plasmaenhanced chemical vapor deposition (“PECVD”), high density PECVD, photonassisted CVD, plasma-photon assisted (“PPACVD”), cryogenic chemicalvapor deposition, chemical assisted vapor deposition, hot-filamentchemical vapor deposition, photo initiated chemical vapor deposition,CVD of a liquid polymer precursor, deposition using supercriticalfluids, or transport polymerization (“TP”). These processes may be usedalone or in combination. In certain preferred embodiments, thedeposition of the barrier layer is conducted at a temperature rangingfrom 100 to 425° C., preferably from 150 to 400° C. In certain otherpreferred embodiments, the deposition is conducted under vacuum at apressure ranging from 10⁻⁹ torr to 400 torr, preferably from 1 millitorrto 100 torr. Although the chemical reagents used herein may be sometimesdescribed as “gaseous”, it is understood that the chemical reagents maybe delivered directly as a gas to the reactor, delivered as a vaporizedliquid, a sublimed solid and/or transported by an inert carrier gas intothe reactor. A reducing gas such as hydrogen can optionally be usedduring the deposition of the barrier layer.

In certain embodiments, PVD processes, such as sputtering, reactivesputtering, etc. may be used to deposit metal nitride, metal carbide,metal carbonitride, metal silicon nitride, metal silicon carbide, ormetal silicon carbonitride barrier layers having a surface with andwithout a (111) preferred orientation. The extent of metal nitride,metal carbide, or metal carbonitride material with (111) preferredorientation present in the film can be adjusted by manipulatingdeposition parameters including the sputtering rate, the applied powerand bias, the partial pressure of reactive gas such as nitrogen, ammoniaor a hydrocarbon gas, the deposition temperature and pressure, etc. Ifthe surface of the barrier layer does not have a substantially (111)preferred orientation or if the surface is comprised of a metal nitride,metal carbide, metal carbonitride or mixture and has less thanstoichiometric amount of nitrogen and/or carbon atoms relative to metalatoms contained therein, the barrier layer can be exposed to an adhesionpromoting agent such as any of the agents disclosed herein prior todepositing the metal by CVD or ALD processes. The exposure to anadhesion promoting agent is preferably conducted at a temperature andpressure similar to that used to deposit the metal nitride, metalcarbide, metal carbonitride, metal silicon nitride, metal siliconcarbide, or metal silicon carbonitride diffusion barrier layer.

A tantalum nitride barrier layer can be deposited by a PVD (orsputtering) process, such as that described in International PatentApplication WO 99/53114 and by Mehrotra in a paper “Properties of DirectCurrent Magnetron Reactively Sputtered TaN” published in J. Vac. Sci.Technology, 1987. If the surface of the PVD (or sputtered) TaN does notcontain TaN with a substantially (111) preferred orientation or has lessthan a stoichiometric amount of nitrogen atoms relative to metal atomscontained therein, the surface may be exposed to an adhesion promotingagent such as nitrogen or plasma activated nitrogen, or any of the otheradhesion promoting agents disclosed herein, prior to forming the metallayer.

A tungsten nitride barrier layer can be deposited by a CVD process, suchas that described in International Patent Application WO 99/00830. Ifthe surface of the CVD deposited WN barrier layer does not contain WNwith a substantially (111) preferred orientation or has less than astoichiometric amount of nitrogen relative to metal contained therein,the surface may be exposed to an adhesion promoting agent such asnitrogen or plasma activated nitrogen, or any of the other adhesionpromoting agents disclosed herein, prior to forming the metal layer.

A titanium nitride barrier layer can be deposited by a PVD (orsputtering) process, such as that described, for example, in JapanesePatent Application 96127870 and U.S. Pat. Nos. 5,521,120; 5,242,860; and5,434,044. The titanium nitride barrier layer may also be deposited by asputtering process such as that described by Chen et al. in a paper“Evaluation of Radio-Frequency Sputtered-Deposited Textured TiN ThinFilms as diffusion Barriers between Copper and Silicon” published in J.Vac. Sci. Technology, 2002 and by Li in a paper “Initial Growth andTexture Formation During Reactive Magnetron Sputtering of TiN onSi(111)” published in J. Vac. Sci. Technology, 2002. If the surface ofthe PVD (or sputtered) TiN does not contain TiN with a substantially(111) preferred orientation or has less than a stoichiometric amount ofnitrogen relative to metal contained therein, the surface may be exposedto an adhesion promoting agent such as nitrogen or plasma activatednitrogen, or any of the other adhesion promoting agents disclosedherein, prior to forming the metal layer.

A titanium nitride barrier layer can be deposited by a CVD process suchas that described, for example, by Weiller in a paper “CVD of TitaniumNitride for Electronic Applications: Gas Phase Chemical Kinetics forFundamental Principles and Modeling” published in ElectrochemicalSociety Proceedings, 1996, by Buiting et al. in a paper “KineticalAspects of the LPCVD of Titanium Nitride from Titanium Tetrachloride andAmmonia” published in J. Electrochem. Society, 1991, and by Boutevillein a paper “Low Temperature Rapid Thermal Low Pressure Chemical VaporDeposition of (111) Oriented TiN Layers from the TiCl₄—NH₃—H₂ GaseousPhase” published in Microelectronic Engineering, 1997. If the surface ofthe CVD deposited TiN does not grow with a substantially (111) preferredorientation or has less than a stoichiometric amount of nitrogenrelative to metal contained therein, the surface may be exposed to anadhesion promoting agent such as nitrogen or plasma activated nitrogen,or any of the other adhesion promoting agents disclosed herein, prior toforming the metal layer.

In embodiments wherein the surface of the barrier layer is exposed to anadhesion promoting agent, the exposure may occur prior to or during atleast a portion (preferably the initial portion) of the formation of themetal film. The temperature of the exposure step is preferably about 40to about 400° C., more preferably 100 to 400° C. The duration of theexposure step may range from about 0.1 to about 10 minutes, or from 0.1to 2 minutes. The pressure during exposure may range from about 10⁻9torr to 400 torr or from 1 millitorr to 100 torr.

As mentioned previously, at least one organometallic precursor is usedto form the metal or copper film using a CVD or an ALD process. Theorganometallic precursor may be used by itself or in a mixture withother organometallic compounds depending upon the composition of themetal film to be deposited. Exemplary organometallic precursor compoundsinclude organometallic copper precursors, organometallic platinumprecursors, organometallic nickel precursors, organometallic cobaltprecursors, organometallic palladium precursors, etc.

In certain embodiments of the present invention, the organometallicprecursor may be a non-fluorinated organometallic compound such as thecompound represented by the structure (I):

In structure (I), M and M′ are each a metal such as Cu, Ag, Au, and Ir;X and X′ can be N or O; Y and Y′ can be Si, C; Sn, Ge, B or Al; and Zand Z′ can be C, N, or O. Substituents represented by R1, R2, R3, R4,R5, R6, R1′, R2′, R3′, R4′, R5′, and R6′ will vary depending on the ringatom to which they are attached. In one embodiment of the presentinvention wherein a copper film is formed, M and M′ are each Cu; X andX′ are each N; Y and Y′ are each Si; Z and Z′ are each C; R1, R2, R1′,and R2′ are each independently an alkyl, an alkenyl, an alkynyl, apartially fluorinated alkyl, an aryl, an alkyl-substituted aryl, apartially fluorinated aryl, a fluoroalkyl-substituted aryl, atrialkylsilyl, or a triarylsilyl; R3, R4, R3′, and R4′ are eachindependently an alkyl, a partially fluorinated alkyl, a trialkylsilyl,a triarylsilyl, a trialkylsiloxy, a triarylsiloxy, an aryl, analkyl-substituted aryl, a partially fluorinated aryl, afluoroalkyl-substituted aryl, or an alkoxy; and R5, R6, R5′, and R6′ areeach independently a hydrogen, an alkyl, an alkenyl, an alkynl, apartially fluorinated alkyl, an aryl, an alkyl-substituted aryl, apartially fluorinated aryl, a fluoralkyl-substituted aryl, atrialkylsilyl, a triarylsilyl, a trialkylsiloxy, triarylsiloxy, analkoxy, a SiR7R8N(R9R10) group, or a SiR7R8OR11 group wherein R7, R8,R9, R10, and R11 can be an alkyl; and the alkyl and alkoxide groups havefrom 1 to 8 carbons, the alkenyl and the alkynyl groups have from 2 to 8carbons; and the aryl group has 6 carbons. Additional examples ofnon-fluorinated organometallic precursors suitable for use with thepresent invention are provided in pending U.S. patent application Ser.No. 10/323,480 and U.S. patent application Ser. No. 10/420,369, whichare presently assigned to the assignee of the present invention.

In certain preferred embodiments of the present invention, at least oneorganometallic copper precursor is used to form a copper film. Theorganometallic copper precursor may be fluorinated or non-fluorinated.Examples of fluorinated compounds include, but are not limited to,compounds comprising hexafluoroacetylacetonate, most preferablyCu(I)(hfac)(tmvs). Examples of non-fluorinated organometallic copperprecursors include, but are not limited to, copper bis(acetylacetanoate), copper bis(2-dimethylaminoethoxide), andtetra(copper tert-butoxide).

The organometallic precursor may be added to the deposition chamber as amixture with other materials. Such materials include carrier gases,which may be employed in transporting the gaseous phase precursors tothe reaction chamber for lesser volatile precursors, and enhance orotherwise control the deposition rate. Examples of other compounds thatcan be added to the deposition chamber include, but are not limited to,H₂O, tmvs, H₂, Ar, He, Kr, or Xe. The metal film of the presentinvention may be deposited using any of the ALD or CVD processesdisclosed herein. Processes disclosed herein may be conducted at ambientpressure or less, or at a pressure ranging from about 10⁻⁹ torr to 400torr. Processes can be conducted at temperatures below room temperatureand at temperatures typically achieved during deposition of barrierlayers. Preferably, the processes are conducted at temperatures rangingfrom 50 to 400° C.

In one embodiment of the present invention, the metal film is formed byan ALD process. An example of an ALD process suitable for use with thepresent invention is provided in pending U.S. patent application Ser.No. 10/324,781. A metal film is deposited upon a substrate surface withthe desired diffusion barrier layer from at least two precursors: ahalogen-containing precursor and a metal-containing precursor. Examplesof suitable halogen-containing precursors include, but are not limitedto, halogen-containing silanes; alkylchlorosilanes, alkylbromosilanes,or alkyliodosilanes; silicon halide compounds such as silicontetrachloride, silicon tetrabromide, or silicon tetraiodide; halogenatedtin compounds such as alkylchlorostannanes, alkylbromostannanes, oralkyliodostannanes; germane compounds such as alkylchlorogermanes,alkylbromogermanes, or alkyliodiogermanes; boron trihalide compoundssuch as boron trichloride, boron tribromide, or boron triodide; aluminumhalide compounds such as aluminum chloride, aluminum bromide, oraluminum iodide; alkylaluminum halides; gallium halide compounds such asgallium trichloride, gallium tribromide, or gallium triodide; orcombinations thereof. Examples of suitable metal-containing precursorsinclude any of the organometallic precursors disclosed herein. A metalhalide layer is grown by sequentially introducing the halogen-containingprecursor and a metal-containing precursor into the process chamber. Themetal halide layer is then exposed to a reducing agent such as, but notlimited to, hydrogen gas, remote hydrogen plasma, silanes, boranes,alanes, germanes, hydrazines, or mixtures thereof.

Thin films may exhibit a range of atomic order from amorphous to highlycrystalline. A crystalline thin film may form as one single crystal witha specific crystallographic orientation relative to the substrate, or asan aggregate of crystals, with random or non-random orientations. XRD iscapable of distinguishing highly oriented single crystals orpolycrystalline films from polycrystalline films with randomorientation. It has been shown that a metal film such as a copper filmhaving (111) as the dominant texture or orientation is preferablebecause of its resistance to electromigration. Furthermore, it is widelyaccepted that a copper film deposited via a CVD process tends to formwith a preference for a (100) orientation on the most commonly utilizedbarrier layers, such as tantalum, while copper deposited via asputtering process on the same barrier layer tends to orient with apreference for a (111) texture which helps to enhance the electricalproperties of the copper. In certain embodiments, the method describedherein not only improves the adhesion of copper but also promotes thegrowth of copper as well as other metal films with a preference for a(111) orientation if deposited onto a (111) oriented barrier layer.

The metal film of the present invention may be a substantiallycontinuous film, preferably having a thickness of at least 5 angstroms,more preferably from 5 to 6000 angstroms. In certain embodiments of thepresent invention, the metal or copper film may be used as aninterfacial layer and/or a seed layer at the top of the barrier layer.

The invention will be illustrated in more detail with reference to thefollowing Examples, but it should be understood that the presentinvention is not deemed to be limited thereto. In this connection, whilethe examples simulate the CVD deposition of a copper film using, it isunderstood that the present invention is suitable for deposition ofother metal films using organometallic precursors besides organometalliccopper precursors by CVD or ALD processes.

EXAMPLES

For the following examples, a number of theoretical calculations wereperformed based on periodic quantum mechanical density function theoryunder the generalized gradient approximation to study reactivity of aCUPRASELECT™ organometallic copper precursor with a variety of differentdiffusion barrier layers. A series of ab initio molecular dynamicsimulations using different barrier layers was performing using thecomputer software program entitled “Siesta” developed by Sanchez-Portal,Ordejon, et al. (Refs. D. Sanchez-Protal, P. Ordejon, E. Artacho, and J.M. Soler, Int. J. Quantum Chem. 65, 453 (1997); J. M. Soler, E. Artacho,J. D. Gale, A. Garcia, J. Junquera, P. Ordejon, and D. Sanchez-Portal,J. Phys. Condens. Matter 14, 2745 (2002). Surface reactions includingcopper deposition were directly simulated. The simulation methods wereentirely base on physical first principles without using empirical orexperimental parameters and have been widely shown to be capable ofproviding accurate thermodynamic and kinetic data for a wide range ofmaterials.

For the following examples, the structure of the Cu(I)(hfac)(tmvs) orCUPRASELECT™ molecule used was as follows:

The tantalum or tungsten barrier layer was simulated by using 3 atomiclayers of tantalum; whereas, the tantalum or tungsten nitride layer wassimulated by using 3 atomic layers of tantalum and 3 atomic layers ofnitrogen.

Example 1 Copper Deposited by CUPRASELECT™ Upon Tantalum Metal BarrierLayer having (100) Preferred Orientation

An ab initio molecular dynamic computer simulation, based on periodicdensity function theory, was used to study the interaction betweenCUPRASELECT™ and a tantalum metal surface with a (100) preferredorientation. The simulation was performed at room temperature (25° C.)and near the CVD copper deposition temperature of 200° C. Thetheoretical results predicted that the CUPRASELECT™ molecule decomposedspontaneously upon exposure to a tantalum metal layer and formedtantalum carbides, oxides, and fluorides. The results also predictedthat the C—CF₃ bond in the ‘hfac’ ligand was the weakest bond within themolecule and can be easily broken into CF₃ groups. The energy requiredto break the C—CF₃ bond is ˜39 kcal/mol, which was considerably lowerthan the exothermic energy (˜260 kcal/mol) involved in the chemisorptionof CF₃ on the tantalum metal surface. This highly exothermic energywould be responsible for the further decomposition of CF₃ intofragments. Rather than volatilizing and escaping the deposition chamber,the fragments react with the tantalum surface, thereby forming afluorine, carbon and oxygen containing amorphous layer on the barrierlayer. This amorphous layer may lower the adherence of a copper layerwhen deposited onto the tantalum metal barrier layer.

Due to the formation of the amorphous layer, the present exampleillustrates that it may be difficult, if not impossible, to depositcopper adherently on tantalum metal by conventional CVD or ALDprocesses. The example also illustrates that the exothermic energyinvolved in chemisorption of the CF₃ radical on a barrier layer could beused indirectly to evaluate the interaction between the CUPRASELECT™molecule and the barrier layer and the adhesion of copper on the barrierlayer in subsequent examples. A high exothermic chemisorption energyresulting in fragmentation of the CF₃ radical would indicate pooradhesion of the copper deposited by CUPRASELECT™ on a barrier layer.

Example 2 Copper Deposited by CUPRASELECT™ Upon Tantalum Nitride BarrierLayer having (100) Orientation

A computer simulation program applying the periodic density functiontheory was used to study the interaction between the CUPRASELECT™molecule and tantalum nitride surface with a (100) preferred orientationand fragments or dissociated species of the CUPRASELECT™ molecule andtantalum nitride surface. The tantalum nitride contained 50:50 tantalumand nitrogen atoms. The tantalum nitride surface with (100) orientation,according to quantum mechanical calculations, contains alternatingtantalum and nitrogen atoms on the surface. This indicates that theCUPRASELECT™ molecule will be exposed to a diffusion barrier surfacecontaining tantalum atoms. Like Example 1, the interaction between theCUPRASELECT™ molecule and the tantalum nitride surface with (100)preferred orientation was determined by the exothermic energy involvedin the chemisorption of the CF₃ radical on the tantalum nitride barrierlayer.

The theoretical results predicted exothermic chemisorption energyof >125 kcal/mol. This energy was noted to be more than sufficient todecompose the CUPRASELECT™ molecule on the tantalum nitride surface withthe (100) preferred orientation and cause reaction between the CF₃radical and the tantalum nitride barrier layer. This would result informing the fluorine, carbon and oxygen containing amorphous layer onthe barrier layer and poor adhesion of CVD or ALD deposited copper onthe barrier layer.

The theoretical results from the computer simulation indicated that theCF₃ radical was selectively adsorbing on the tantalum atoms, decomposinginto further fragments, and then reacting with the tantalum atoms.Interestingly, however, no adsorption of the CF₃ radical was observed onthe nitrogen atoms. These results indicated that exposure of tantalumatoms was responsible for the exothermic chemisorption and decompositionof the CF₃ radical on the tantalum nitride surface with (100) preferredorientation. This example revealed that it would not be technicallyfeasible to deposit copper adherently on tantalum nitride surface with(100) preferred orientation as long as tantalum atoms are exposed to theCUPRASELECT™ molecule and its fragments.

Example 3 Copper Deposited by CUPRASELECT™ Upon Tantalum Nitride BarrierLayer having a Substantially (111) Preferred Orientation

A computer simulation program applying the periodic density functiontheory was used to study the interaction between the CUPRASELECT™molecule and tantalum nitride surface with a substantially (111)preferred orientation and fragments or dissociated species of theCUPRASELECT™ molecule and tantalum nitride surface. The tantalum nitridecontained 50:50 tantalum and nitrogen atoms. The tantalum nitridesurface with a substantially (111) preferred orientation, according toquantum mechanical calculations, contains tantalum atoms that arelocated underneath the nitrogen atoms. This means that the CUPRASELECT™molecule will not be directly exposed to tantalum atoms. Like theprevious examples, the interaction between the CUPRASELECT™ molecule andthe tantalum nitride surface with (111) preferred orientation wasdetermined by the exothermic energy involved in adsorbing the CF₃radical on the tantalum nitride barrier layer.

The theoretical results predicted exothermic chemisorption energy of <55kcal/mol, which is insufficient to overcome the activation barrier tobreak the C—CF₃ bond in the CUPRASELECT™ molecule.

A more careful look into the theoretical results indicated that the CF₃radicals were not adsorbed onto the tantalum nitride surface with asubstantially (111) preferred orientation. In fact, the computersimulation showed that the CF₃ radicals were repelled from the surface.This example revealed that it would be technically feasible to depositcopper adherently on tantalum nitride surface with a substantially (111)orientation. It also revealed that it would be technically feasible todeposit copper adherently on tantalum nitride surface as long astantalum atoms are not exposed to the CUPRASELECT™ molecule.

Example 4 Copper Deposited by CUPRASELECT™ Upon Tantalum Nitride BarrierLayer having (100) Preferred Orientation after Exposure to Nitrogen Gas

A computer simulation program applying the periodic density functiontheory was used to study the interaction between the CUPRASELECT™molecule and tantalum nitride surface with (100) preferred orientationafter exposure to nitrogen gas. The tantalum nitride contained 50:50tantalum and nitrogen atoms. The interaction between nitrogen gas andtantalum nitride surface with (100) preferred orientation was determinedby the exothermic energy involved in chemisorption of nitrogen on thetantalum nitride barrier layer.

The theoretical results predicted exothermic chemisorption energy of >97kcal/mol. This energy was more than sufficient to passivate the tantalumnitride surface with (100) preferred orientation with nitrogen as wellas burying tantalum atoms under the nitrogen atoms. This meant that atantalum nitride surface with (100) preferred orientation after exposureto an adhesion promoting agent such as nitrogen would not react with anydissociated CF₃ radicals. As a result, the formation of fluorine, carbonand oxygen-containing amorphous layer on the barrier layer would beavoided thereby providing good adhesion of CVD or ALD deposited copperon the barrier layer.

This example revealed that it would be technically feasible to depositcopper adherently on tantalum nitride surface with (100) preferredorientation provided that the tantalum nitride surface is pretreatedwith an adhesion promoting agent such as nitrogen prior to exposing itto the CUPRASELECT™ molecule and its fragments.

Example 5 Copper Deposited by CUPRASELECT™ Upon Tantalum Nitride BarrierLayer having a Substantially (111) Preferred Orientation

A computer simulation program applying the periodic density functiontheory was used to study the interaction between the CUPRASELECT™molecule and tantalum nitride surface with a substantially (111)preferred orientation. The simulation was performed at room temperature(25° C.) and near the CVD copper deposition temperature of 200° C. Thetheoretical results predicted that the CUPRASELECT™ molecule cleanlydeposited copper on the surface without decomposition of the ‘hfac’ligand and the protecting olefinic species. The results also revealedthat the remaining components of the CUPRASELECT™ molecule did notinteract with the surface and were readily removed from the surface inthe form of a gas.

This example confirmed the results described in Example 3. Furthermore,it confirmed that it would be technically feasible to deposit copperadherently on tantalum nitride surface with a substantially (111)preferred orientation.

Example 6 Copper Deposited by CUPRASELECT™ Upon Tungsten Barrier Layerhaving (100) Preferred Orientation

A computer simulation program applying the periodic density functiontheory was used to study the interaction between the CUPRASELECT™molecule and tungsten surface with a (100) preferred orientation andfragments or dissociated species of the CUPRASELECT™ molecule andtungsten surface. The theoretical results predicted that CUPRASELECT™molecule decomposed spontaneously upon exposing to tungsten metal. Theenergy of 39 kcal/mol required to break the C—CF₃ bond within the ‘hfac’ligand was considerably lower than the exothermic energy (˜272.7kcal/mol) involved in the chemisorption of the CF₃ radical on thetungsten surface. This highly exothermic energy would be responsible forthe further decomposition of the CF₃ radical into fragments. Rather thanvolatilizing and escaping the deposition chamber, the fragments reactwith the tungsten surface, thereby forming a fluorine, carbon and oxygencontaining amorphous layer on the barrier layer. This amorphous layermay lower the adherence of a copper layer when deposited onto thetantalum barrier layer.

Due to the formation of the amorphous layer, the present exampleillustrates that it may be difficult, if not impossible, to depositcopper adherently on tungsten by conventional CVD or ALD processes.

Example 7 Copper Deposited by CUPRASELECT™ Upon Tungsten Nitride BarrierLayer having a Substantially (111) Preferred Orientation

A computer simulation program applying the periodic density functiontheory was used to study the interaction between the CUPRASELECT™molecule and tungsten nitride surface with a substantially (111)preferred orientation and fragments or dissociated species of theCUPRASELECT™ molecule and tungsten nitride surface. The tungsten nitridecontained 50:50 tungsten and nitrogen atoms with the top layer tungstenatoms fully covered by a monolayer of nitrogen atoms. This means thatthe CUPRASELECT™ molecule will not be directly exposed to tungstenatoms. Like the previous examples, the interaction between theCUPRASELECT™ molecule and the tungsten nitride surface with asubstantially (111) preferred orientation was determined by theexothermic energy involved in adsorbing the CF₃ radical on the tungstennitride barrier layer.

The theoretical results predicted exothermic chemisorption energy of<57.4 kcal/mol. This energy was noted not to be sufficiently high toovercome the activation barrier to break the C—CF₃ bond in theCUPRASELECT™ molecule. This meant that the tungsten nitride surface witha substantially (111) preferred orientation would not facilitatereaction between the CF₃ radical and the tungsten nitride barrier layer.This would result in avoiding the formation of fluorine, carbon andoxygen containing amorphous layer on the barrier layer and providinggood adhesion of CVD copper on the barrier layer.

This example revealed that it would be technically feasible to depositcopper adherently on tungsten nitride surface with a substantially (111)preferred orientation. It also revealed that it would be technicallyfeasible to deposit copper adherently on tungsten nitride surface aslong as tungsten atoms are not exposed to the CUPRASELECT™ molecule.

Example 8 Copper Deposited by CUPRASELECT™ Upon Tungsten Barrier Layerhaving a (100) Preferred Orientation

A computer simulation program applying the periodic density functiontheory was used to study the interaction between (1) CUPRASELECT™ andtungsten surface with (100) preferred orientation and (2) fragments ofCUPRASELECT™ molecule and tungsten surface with (100) preferredorientation. The theoretical results predicted that CUPRASELECT™molecule decomposed spontaneously upon exposing to tungsten metal. Theenergy of 39 kcal/mol required for breaking the C—CF₃ bond wasconsiderably lower than the exothermic energy (˜272.7 kcal/mol) involvedin the chemisorption of the CF₃ radical on the tungsten surface. Thishighly exothermic energy would be responsible for the furtherdecomposition of CF₃ radical into fragments and subsequent reaction withthe tungsten surface, thereby forming fluorine, carbon and oxygencontaining amorphous layer on the barrier layer.

This example revealed that it would not be technically feasible todeposit copper adherently on tungsten.

Example 9 Copper Deposited by CUPRASELECT™ Upon Stoichiometric TungstenNitride Barrier Layer having a (111) Preferred Orientation

A computer simulation program applying the periodic density functiontheory described in Example 7 was repeated to study the interactionbetween CUPRASELECT™ and stoichiometric tungsten nitride surface with(111) preferred orientation. The stoichiometric tungsten nitridecontained 50:50 tungsten and nitrogen atoms. Upon full surface energyrelaxation, the tungsten nitride surface with (111) preferredorientation was noted to undergo significant surface reconstruction,resulting in 2-dimensional hexagonal cells of alternating tungsten andnitrogen layers. Therefore, it could be concluded that the tungstennitride surface with (111) preferred orientation was energeticallyunstable. The reconstructed structure of tungsten nitride contained thelayer of tungsten atoms fully covered by a monolayer of nitrogen atoms.Therefore, the CUPRASELECT™ molecule would not be directly exposed totungsten atoms.

The reactivity of CUPRASELECT™ on the reconstructed surface wasdetermined by following the time evolution of molecular trajectories ofCUPRASELECT™ on the reconstructed tungsten nitride surface under thedeposition conditions, using ab initio molecular dynamics simulations.The possibility of adsorbing the ligands from CUPRASELECT™ on thereconstructed tungsten nitride surface was also examined.

The theoretical results predicted that the CUPRASELECT™ precursorrapidly approached the surface with the copper atom interacting stronglywith the top layer of nitrogen atoms at the four-fold hollow site of thereconstructed tungsten nitride surface. The ligands of CUPRASELECT™remained in the gas-phase and did not decompose upon copper deposition.Adsorption studies indicated that the ligands would essentially berepelled from the reconstructed tungsten nitride surface due to therepulsion between the electron-rich nitrogen layer and the lack ofelectron-deficient groups in the ligands. The results also revealed thatthere was no spontaneous decomposition of the CUPRASELECT™ molecule.

The above simulations results indicated that the tungsten nitridesurface with (111) preferred orientation or reconstructed surface oftungsten nitride with (111) preferred orientation would not facilitatereaction between the ligand of CUPRASELECT™ and tungsten nitride barrierlayer. It would result in avoiding the formation of fluorine, carbon andoxygen containing amorphous layer on the barrier layer and providinggood adhesion of CVD copper on the tungsten nitride barrier layer with(111) preferred orientation or reconstructed surface of tungsten nitridewith (111) preferred orientation.

This example revealed that the tungsten nitride surface with (111)preferred orientation underwent significant surface reconstruction undercopper deposition conditions. This surface reconstruction prevented theexposure of CUPRASELECT™ molecule directly to tungsten atoms.Consequently, it would be technically feasible to deposit copperadherently on tungsten nitride surface with (111) orientation. It alsorevealed that it would be technically feasible to deposit copperadherently on tungsten nitride surface as long as tungsten atoms are notexposed to the CUPRASELECT™ molecule.

Example 10 Copper Deposited by CUPRASELECT™ Upon Stoichiometric TungstenNitride Barrier Layer having a (100) Preferred Orientation

A computer simulation program applying the periodic density functiontheory was used to study the interaction between CUPRASELECT™ andtungsten nitride surface with (100) preferred orientation. Thestoichiometric tungsten nitride contained 50:50 tungsten and nitrogenatoms. The stoichiometric tungsten nitride surface with (100) preferredorientation was formed from the 2-dimensional hexagonal cells ofalternating tungsten layer and nitrogen layer with nitrogen layer on thetop. This meant that the top layer of tungsten atoms was fully coveredby a monolayer of nitrogen atoms. Therefore, the CUPRASELECT™ moleculewould not be directly exposed to tungsten atoms. The first-principlesbased molecular dynamics simulations were performed to investigate thebehavior of CUPRASELECT™ on the tungsten nitride surface with (100)preferred orientation under the deposition conditions.

Two different initial orientations of the precursor were used in themolecular dynamics simulations. In the first orientation theCUPRASELECT™ molecule contacted the tungsten nitride (100) surfacehorizontally. In this orientation, the precursor rapidly approached thesurface with the copper atom interacting strongly with the top layer ofnitrogen atoms at the four-fold hollow site. The copper atom thenanchored strongly at the surface by four nitrogen atoms. The ligands ofthe CUPRASELECT™ complex remained above the surface. There was nospontaneous decomposition of the CUPRASELECT™ molecule. In the secondorientation, the CUPRASELECT™ molecule contacted the tungsten nitride(100) surface vertically. Again, the precursor complex rapidlyapproached the surface with the copper atom anchored at the four-foldhollow site on the top layer of nitrogen. Strong repulsion between thetop nitrogen layer and the ligands, hexafluoracetylacetone (hfac) andtrimethylvinylsilane, were observed in the molecular dynamicstrajectory, indicating minimum reactivity between the ligands and thesurface.

The above simulations results indicated that the tungsten nitridesurface with (100) preferred orientation would not facilitate reactionbetween the ligand of CUPRASELECT™ and tungsten nitride barrier layer.It would result in avoiding the formation of fluorine, carbon and oxygencontaining amorphous layer on the barrier layer and providing goodadhesion of CVD copper on the tungsten nitride barrier layer with (100)preferred orientation.

While the invention has been described in detail and with reference tospecific examples thereof, it will be apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A process for forming a metal film on at least one surface of adiffusion barrier layer comprising tungsten nitride, the processcomprising: providing at least one surface of the diffusion barrierlayer wherein the at least one surface comprises a stoichiometric amountor greater of nitrogen relative to tungsten contained therein andwherein the at least one surface is comprised of an orientation selectedfrom the group consisting of a (111) preferred orientation and a (100)preferred orientation; and forming the metal film via a chemical vapordeposition process on the at least one surface using at least oneorganometallic precursor comprising copper.
 2. The process of claim 1wherein the at least one surface is comprised of non-stoichiometrictungsten nitride having a greater amount of nitrogen atoms than tungstenatoms contained therein.
 3. The process of claim 1 wherein the chemicalvapor deposition is at least one process selected from the groupconsisting of thermal chemical vapor deposition, plasma enhancedchemical vapor deposition, remote plasma enhanced chemical vapordeposition, plasma assisted chemical vapor deposition, cryogenicchemical vapor deposition, chemical assisted vapor deposition,hot-filament chemical vapor deposition, photo-initiated chemical vapordeposition, and combinations thereof.
 4. The process of claim 1 whereinthe at least one organometallic precursor comprises1,1,1,5,5,5-hexafluoro-2,4-pentanedionato-copper (I)trimethylvinylsilane.
 5. The process of claim 1 wherein the at least oneorganometallic precursor comprises a compound represented by thefollowing structure:

wherein M and M′ are Cu; X and X′ are each N or O; Y and Y′ are each Si,C, Sn, Ge, B, or Al; Z and Z′ are each C, N, or O; R1, R2, R1′, and R2′are each independently a hydrogen, an alkyl, an alkenyl, an alkynyl, apartially fluorinated alkyl, an aryl, an alkyl-substituted aryl, apartially fluorinated aryl, a fluoralkyl-substituted aryl, atrialkylsilyl, or a triarylsilyl when X and X′ are N; R1 and R1′ areeach independently an alkyl, an alkenyl, an alkynyl, a partiallyfluorinated alkyl, an aryl, an alkyl-substituted aryl, a partiallyfluorinated aryl, a fluoralkyl-substituted aryl, a trialkylsilyl, or atriarylsilyl when X and X′ are O; R3, R4, R3′, and R4′ are eachindependently a hydrogen, an alkyl, a partially fluorinated alkyl, atrialkylsilyl, a triarylsilyl, a trialkylsiloxy, a triarylsiloxy, anaryl, an alkyl-substituted aryl, a partially fluorinated aryl, afluoroalkyl-substituted aryl, or an alkoxy; and R5, R6, R5′, and R6′ areeach independently a hydrogen, an alkyl, an alkenyl, an alkynyl, apartially fluorinated alkyl, an aryl, an alkyl-substituted aryl, apartially fluorinated aryl, a fluoralkyl-substituted aryl, atrialkylsiloxy, a triarylsiloxy, a trialkylsilyl, a triarylsilyl, or analkoxy; provided that when X and X′ are each O, there is no substitutionat R2 and R2′; further provided that when Z and Z′ are each N, there isno substitution at R6 and R6′; further provided that when Z and Z′ areeach O, there is no substitution at R5, R6, R5′, or R6′; said alkyl andalkoxide having 1 to 8 carbons; said alkenyl and alkynyl having 2 to 8carbons; and said aryl having 6 carbons.
 6. The process of claim 1wherein the metal film is a seed layer.
 7. The process of claim 1wherein the at least one surface is comprised of the (111) preferredorientation.
 8. The process of claim 1 wherein the at least one surfaceis comprised of the (100) preferred orientation.
 9. A process forforming a substantially continuous copper film on a surface of atungsten nitride diffusion barrier layer, the process comprising thesteps of: providing a substrate comprising the surface of the diffusionbarrier layer wherein the surface is selected from a non-stoichiometricsurface comprising a lesser amount of nitrogen atoms than tungsten atomscontained therein, an amorphous surface, a polycrystalline surface, astoichiometric surface having a preferred orientation other than a (100)orientation, a stoiciometric surface having a preferred orientationother than a (111) preferred orientation, and combinations thereof;exposing the surface of the diffusion barrier layer to an at least oneadhesion promoting agent comprising nitrogen; and forming the copperfilm directly on at least a portion of the surface using anorganometallic copper precursor wherein at least a portion of theexposing step is conducted prior to the forming step.
 10. The process ofclaim 9 wherein the surface is the non-stoichiometric surface comprisinga lesser amount of nitrogen atoms than tungsten atoms contained therein.11. The process of claim 9 wherein the surface is amorphous.
 12. Theprocess of claim 9 wherein the surface is polycrystalline.
 13. A processfor forming a substantially continuous metal film on a surface of adiffusion barrier layer, the process comprising: depositing thediffusion barrier layer onto a substrate wherein the surface of thediffusion barrier layer is comprised of at least one material selectedfrom a stoichiometric tungsten nitride with a (100) preferredorientation, a stoichiometric tungsten nitride with a substantially(111) preferred orientation, a stoichiometric tungsten nitride with a(111) preferred orientation, a stoichiometric tungsten nitride which isamorphous, a stoichiometric tungsten nitride which is polycrystalline, anon-stoichiometric tungsten nitride having a greater amount of nitrogenatoms than tungsten atoms contained therein, and a mixture thereof; andforming the metal film on at least a portion of the surface using an atleast one organometallic precursor.
 14. The process of claim 13 whereinthe surface is comprised of stoichiometric tungsten nitride with a (100)preferred orientation.
 15. The process of claim 13 wherein the surfaceis comprised of stoichiometric tungsten nitride with a (111) preferredorientation.
 16. The process of claim 13 wherein the surface iscomprised of non-stoichiometric tungsten nitride having a greater amountof nitrogen atoms than tungsten atoms contained therein.